1. Field of the Invention
The present invention relates to a liquid ejection head and a method of manufacturing same, and more particularly, to a liquid ejection head and a method of manufacturing same, wherein the liquid ejection surface opposing the side face of a rotating drum has a curved shape in the circumferential direction of the rotating drum.
2. Description of the Related Art
As an image forming apparatus, an inkjet printer (inkjet recording apparatus) is known, which comprises an inkjet head (liquid ejection head) having an arrangement of a plurality of nozzles (ejection ports) and which records images on a recording medium by ejecting ink (liquid) from the nozzles toward the recording medium while the inkjet head and the recording medium are caused to be moved relatively to each other.
In an inkjet recording printer, one image is formed on a recording medium by combining dots created by ink ejected from the nozzles. In recent years, it has become desirable to form images of high quality on a par with photographic prints, in inkjet printers. It has been thought that high image quality can be achieved by reducing the size of the ink droplets ejected from the nozzles by reducing the diameter of the nozzles and also increasing the number of pixels per unit surface area by arranging the nozzles at high density. On the other hand, since increasing the density of the nozzles and arranging a large number of nozzles can cause an increase in the size of the apparatus, various methods have been proposed for making the apparatus more compact.
For instance, Japanese Patent Application Publication No. 2002-166543 discloses an inkjet head in which it is sought to make an inkjet head compact in size, by forming ink pressure chambers in an approximately diamond shape, forming ink supply ports in one of the obtuse corner sections of the diamond-shaped pressure chambers, forming an ink spraying nozzle in the other obtuse corner section, arranging the pressure chambers in a plurality of columns, and positioning the pressure chambers in each column in such a manner that the obtuse corner sections on the spray nozzle side are interposed respectively between the pressure chambers in the neighboring column, thereby achieving a high density arrangement of the nozzles.
Furthermore, Japanese Patent Application Publication No. 2000-190535 discloses a recording apparatus having an intermediate transfer body, for instance. An example of the recording apparatus is known in which the image forming apparatus is made compact in size, by holding a recording sheet in a fixed fashion on the surface of a rotating cylindrical tube and providing a plurality of print heads which are movable in the axial direction of the cylinder, in such a manner that an image is formed on the recording sheet by the print heads.
Moreover, for example, Japanese Patent Application Publication No. 2004-50449 discloses a recording apparatus which records images by forming an inverted image by depositing ink droplets on an intermediate transfer body and then transferring the image onto a recording medium. In the recording apparatus, it is sought to improve the quality of the recorded image, by providing a liquid-repelling section in the intermediate transfer body so that aggregation and movement of the each liquid ink droplet on the surface of the intermediate transfer body are suppressed, and by transferring the inverted image formed by the ink droplets deposited on a section of the intermediate transfer body other than the liquid-repelling section, onto the recording medium.
However, the related art technology involves possibilities such as the following. In the case of Japanese Patent Application Publication No. 2002-166543, for example, it is sought to compactify a two-dimensional matrix type head by arranging diamond-shaped pressure chambers at a high density; however, if a matrix head for high-density recording is used in particular, then any rotational deviation of the recording medium due to skewed travel, or the like (namely, inclination of the conveyance direction of the recording medium with respect to the head) is liable to produce deviation in the positions of the ejected droplets, especially at the return sections in the matrix arrangement, since recording is performed while the recording medium is conveyed.
For example, in the case of a high-density inkjet head 950 in which nozzles 951 are arranged in a two-dimensional matrix configuration as shown in FIGS. 20A to 20C, dots 961 are formed on a recording medium 960 by ejecting ink droplets from the nozzles 951 while the recording medium 960 is conveyed relatively with respect to the head.
In this case, if the recording medium 960 is conveyed correctly in a perfectly straight direction with respect to the inkjet head 950, as shown in FIG. 20A, then dots 961 are formed at correct positions on the recording medium 960. However, if the recording medium 960 is conveyed in a skewed fashion, and is inclined toward the left-hand side with respect to the inkjet head 950, as shown in FIG. 20B, then the dot pitch would become narrower and the dots 961 might overlap at the return points of the nozzle columns, as indicated by reference numeral 962 in FIG. 20B, whereas the pitch between the dots 961 would become greater in other positions.
Furthermore, if the recording medium 960 is conveyed in a skewed fashion, and is inclined toward the right-hand side with respect to the inkjet head 950, as shown in FIG. 20C, then the pitch between the dots 961 would become greater at the return points of the nozzle columns, as indicated by reference numeral 964 in FIG. 20C, whereas the pitch between the dots 961 would become narrower in the other positions.
In this way, in an inkjet head in which the nozzles are arranged at high density in a two-dimensional matrix configuration, if the recording medium is conveyed in a skewed fashion, then the positions of the dots formed on the recording medium become disarranged, thus causing band-shaped non-uniformities, and the like, and hence degrading the image quality. In addition to cases where the recording medium is conveyed in a skewed fashion, the same type of possibility might occurs in cases where the inkjet head is installed in an inclined fashion, since this produces a similar positional relationship between the inkjet head and the recording medium. Moreover, in a flat conveyance system, the recording medium is liable to float up, or create projections, variations in thickness, or the like. Therefore, in those cases, it is difficult to reduce the gap between the nozzles and the recording medium, and variation in the landing positions due to deviation in the flight of the droplets can become larger.
Furthermore, the apparatus disclosed in Japanese Patent Application Publication No. 2000-190535, is made compact in size by disposing heads in the circumferential direction of a cylinder; however, this has a structure in which line heads are installed on a curved face-shaped member, and hence it is difficult to apply this type of composition to a matrix type head in which a plurality of nozzles are arranged at high density in a two-dimensional configuration.
Furthermore, Japanese Patent Application Publication No. 2004-50449 seeks to achieve improved image quality by providing a very fine liquid-repelling section on the surface of an intermediate transfer roller; however, in a line type head such as the embodiments illustrated in the publication, semiconductor processing is required and it becomes difficult to achieve a long length and high-speed operation, and in a head composed by joining together a plurality of short heads, non-uniformity density is liable to occur at an area corresponding to a joint section between the heads, and hence such heads are not very suitable for high-quality recording. Moreover, in a matrix type head having a long, single-body structure, since the head is required to have a certain length in the circumferential direction, then the gap between the drum and the nozzles is not uniform if the nozzle surface of the head is a flat surface, and therefore, practical application is difficult.